Lithium-ion batteries (LIBs) have attracted extensive attention in the past two decades for a wide range of applications in portable electronic devices such as cellular phones and laptop computers. Due to rapid market development of electric vehicles (EV) and grid energy storage, high-performance, low-cost LIBs are currently offering one of the most promising options for large-scale energy storage devices.
In general, a lithium ion battery includes a separator, a cathode and an anode. Currently, electrodes are prepared by dispersing fine powders of an active battery electrode material, a conductive agent, and a binder material in an appropriate solvent. The dispersion can be coated onto a current collector such as a copper or aluminum metal foil, and then dried at an elevated temperature to remove the solvent. Sheets of the cathode and anode are subsequently stacked or rolled with the separator separating the cathode and anode to form a battery.
Polyvinylidene fluoride (PVDF) has been the most widely used binder materials for both cathode and anode electrodes. Compared to non-PVDF binder materials, PVDF provides a good electrochemical stability and high adhesion to the electrode materials and current collectors. However, PVDF can only dissolve in some specific organic solvents such as N-Methyl-2-pyrrolidone (NMP) which requires specific handling, production standards and recycling of the organic solvents in an environmentally-friendly way. This will incur significant costs in the manufacturing process.
The use of aqueous solutions instead of organic solvents is preferred for environmental and handling reasons and therefore water-based slurries have been considered. Water soluble binders such as carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) have been attempted. However, CMC and SBR are generally limited to anode applications.
U.S. Pat. No. 8,956,688 B2 describes a method of making a battery electrode. The method comprises measuring the zeta potential of the active electrode material and the conductive additive material; selecting a cationic or anionic dispersant based on the zeta potential; determining the isoelectric point (IEP) of the active electrode material and the conductive additive material; dispersing an active electrode material and a conductive additive in water with at least one dispersant to create a mixed dispersion; treating a surface of a current collector to raise the surface energy of the surface to at least the surface tension of the mixed dispersion; depositing the dispersed active electrode material and conductive additive on a current collector; and heating the coated surface to remove water from the coating. However, the method is complicated, involving measurements of the zeta potential of the active electrode material and the conductive additive material, and isoelectric point (IEP) of the active electrode material and the conductive additive material. Furthermore, an additional surface treatment step for treating the surface of the current collector is required in order to enhance the capacity retention.
U.S. Pat. No. 8,092,557 B2 describes a method of making an electrode for a rechargeable lithium ion battery using a water-based slurry having a pH between 7.0 and 11.7, wherein the electrode includes an electro-active material, a (polystyrenebutadiene rubber)-poly (acrylonitrile-co-acrylamide) polymer, and a conductive additive. However, this method does not provide any data for evaluating the electrochemical performance of the electrodes prepared by this method.
U.S. Patent Application No. 2013/0034651 A1 describes a slurry for the manufacture of an electrode, wherein the slurry comprises a combination of at least three of polyacrylic acid (PAA), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) and polyvinylidene fluoride (PVDF) in an aqueous solution and an electrochemically activatable compound. However, the slurry for preparing the cathode electrode comprises acetone or other organic solvents such as NMP and DMAC.
In view of the above, there is always a need to develop a method for preparing cathode and anode electrodes for lithium-ion battery using a simple, inexpensive and environmentally friendly method.